Superposition model analysis of the short-range ordering for Mn²⁺in oxide glasses

Abstract

The superposition model is employed to account for the fine-structure parameters for Mn2+ in oxide glasses determined recently by computer simulations of g=2.0 and g=4.3 resonances. Analytic expressions relating distributions of the fine-structure parameters D and E to distributions of ligand coordinates are obtained for sixfold and fourfold coordinations of Mn2+. Quantitative estimates are made of mean distortion parameters and root-mean-square variations of interatomic distances and angles in the environment of Mn2+. It is shown that both the mean distortions from cubic symmetry and the degree of short-range disorder are considerably smaller for the g=2.0 sites than for the g=4.3 sites. A possibility of attributing the g=2.0 and g=4.3 resonances to Mn2+ ions substituting respectively for network modifiers and network formers in the oxide glasses is discussed.

Vibrational spectra of olivine composition glasses: The Mg-Mn join

“…Additionally, electron spin resonance spectra of Mn 2 + in oxide glasses demonstrate that manganese may be presei~.t in both network-forming and network modifying sites (Kliava 1982). Indeed, that the Mn 2+ ion becomes more covalently bound in glasses as the number of nonbridging oxygens per silicate tetrahedron (NBO/T) increases from 0.5 to 2.0 has been documented using optical absorption spectra (Nelson and White 1980;Nelson et al 1983).…”

EPE of impurity ions in disordered solids distributions of the spin hamiltonian parameters

“…Then the transformation of (4.1) can be applied t o obtain the relations between the mean fs parameters Do and E,, and mean distortions of the first coordination shell, as well as between AD and AE and the root-meansquare deviations of the ligand coordinates, respectively, AR,, Ae,, and Aq, for the radial, polar, and azimuthal coordinates of the ligand j . These two types of relations have been obtained in [138] for several cases of fourfold and sixfold coordinations (most often inferred for paramagnetic ions in disordered media) with rhombic average distortions from cubic symmetry classified in terms of the group theory and shown in Fig. 10 a to e. For reference, we list these relations below, in a somewhat simplified form.…”

“…Brodbeck and Bukrey [137] and Kliava [138] applied this model t o disordered solids; the latter work offers a more general treatment, concerning not only average configurations of the nearest-neighbour ligands but also the short-range disorder parameters inherent in the amorphous state of matter. In order to account for randomness in the environment of paramagnetic ions, it is assumed that the coordinates of all ligands are subject t o random small variations (presumably, these variations are independent and governed by the Gaussian distributions).…”

ChemInform Abstract: EPR of Impurity Ions in Disordered Solids. Distributions of the Spin Hamiltonian Parameters

“…For both d5 and f 7 group ions the semiempirical superposition model [135, 1361 has been widely used to analyse their atomic surroundings in various crystalline hosts. Brodbeck and Bukrey [137] and Kliava [138] applied this model t o disordered solids; the latter work offers a more general treatment, concerning not only average configurations of the nearest-neighbour ligands but also the short-range disorder parameters inherent in the amorphous state of matter. In order to account for randomness in the environment of paramagnetic ions, it is assumed that the coordinates of all ligands are subject t o random small variations (presumably, these variations are independent and governed by the Gaussian distributions).…”